Just played around a bit, I don't really know if this will help much, but replacing the
RotateEntity camera,Sin(MilliSecs()*.05)*.5,0,Sin(MilliSecs()*.05)*.5
with
TurnEntity camera, Sin(MilliSecs()*.05)*.0075, 0, Sin(MilliSecs()*.05)*.0075
seems to give about the same rocking motion, while allowing the mouse look.
RotateEntity camera,Sin(MilliSecs()*.05)*.5,0,Sin(MilliSecs()*.05)*.5
with
TurnEntity camera, Sin(MilliSecs()*.05)*.0075, 0, Sin(MilliSecs()*.05)*.0075
seems to give about the same rocking motion, while allowing the mouse look.